Red light-emitting fluorescent substance and light-emitting device employing the same

ABSTRACT

The embodiment provides a red light-emitting fluorescent substance represented by the following formula (1):
 
(M 1-x EC x ) a M 1   b AlO c N d   (1).
 
In the formula (1), M is an element selected from the group consisting of IA group elements, IIA group elements, IIIA group elements, IIIB group elements, rare earth elements and IVA group elements; EC is an element selected from the group consisting of Eu, Ce, Mn, Tb, Yb, Dy, Sm, Tm, Pr, Nd, Pm, Ho, Er, Cr, Sn, Cu, Zn, As, Ag, Cd, Sb, Au, Hg, Tl, Pb, Bi and Fe; M 1  is different from M and is selected from the group consisting of tetravalent elements; and x, a, b, c and d are numbers satisfying the conditions of 0&lt;x&lt;0.2, 0.63&lt;a&lt;0.80, 2.1&lt;b&lt;2.63, 0&lt;c≦0.24 and 4&lt;d&lt;5, respectively. This substance emits luminescence having a peak in the wavelength range of 620 to 670 nm when excited by light of 250 to 500 nm.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 13/037,635filed Mar. 1, 2011, now U.S. Pat. No. 8,414,795 and is based upon andclaims the benefit of priority from the prior Japanese PatentApplication No. 2010-201710, filed on Sep. 9, 2010; the entire contentsof which are incorporated herein by reference.

FIELD

The embodiments relate to a red light-emitting fluorescent substance anda light-emitting device.

BACKGROUND

There is a recently developed white light-emitting LED device thatcomprises a blue LED and a yellow phosphor in combination. For thepurpose of expanding new markets, this device is studied for use as anillumination light or a backlight source of liquid crystal display.However, since the light emitted by the device is a mixture of blueemission from the blue LED and luminescence from the yellow phosphor,the device gives “pseudo-white” color light, which is lacking in redcolor. Accordingly, from the viewpoint of color rendition, there is roomfor improvement. In view of this, a new white light-emitting LED deviceis proposed that comprises a red light-emitting fluorescent substance inaddition to the blue LED and yellow phosphor, and the red light-emittingfluorescent substance used therein is being vigorously researched inthese days.

Meanwhile, it has been more and more required for the whitelight-emitting LED device to be improved in luminance. To meet thisrequirement, increased electric power is often applied to the device andaccordingly the device operating temperature is apt to riseconsiderably. When the device works at a high temperature, the emissionefficiency generally drops that the expected luminance often cannot beobtained and/or that the luminance balance among the fluorescentsubstances may be lost to cause color discrepancies. Also from thispoint of view, it is desired to provide a fluorescent substanceexcellent both in luminance and in temperature characteristics.

Further, according to increased demand for high color rendition, varioustypes of the white light-emitting LED device have been developed andcommercially sold for lighting purposes or the like. The color renditionis often evaluated in terms of the general color rendering index (Ra),and hence it is desired to provide a high color rendering light-emittingdevice giving a high Ra value. On the other hand, for application todisplays, it is desired to provide a white light-emitting LED devicehaving both a wide gamut of reproducible colors (NTSC ratio) and a highefficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a vertical sectional view schematically illustrating alight-emitting device according to one aspect of the embodiment.

FIG. 2 is an XRD profile of the red fluorescent substance produced inExample 1.

FIG. 3 shows an emission spectrum of the red fluorescent substanceproduced in Example 1 under excitation with a blue LED.

FIG. 4 shows an emission spectrum of the red fluorescent substanceproduced in Example 2 under excitation with a blue LED.

FIG. 5 is an XRD profile of the red fluorescent substance produced inExample 3.

FIG. 6 shows an emission spectrum of the red fluorescent substanceproduced in Example 3 under excitation by light at 365 nm.

FIG. 7 shows an emission spectrum of the red fluorescent substanceproduced in Example 3 under excitation with a blue LED.

FIG. 8 shows an emission spectrum of the red fluorescent substanceproduced in Example 4 under excitation by light at 365 nm.

FIG. 9 shows an emission spectrum of the red fluorescent substanceproduced in Example 4 under excitation with a blue LED.

FIG. 10 shows an emission spectrum of the red fluorescent substanceproduced in Example 5 under excitation by light at 365 nm.

FIG. 11 shows an emission spectrum of the red fluorescent substanceproduced in Example 5 under excitation with a blue LED.

FIG. 12 shows an emission spectrum of the red fluorescent substanceproduced in Example 6 under excitation by light at 365 nm.

FIG. 13 shows an emission spectrum of the red fluorescent substanceproduced in Example 6 under excitation with a blue LED.

FIG. 14 shows an emission spectrum of the red fluorescent substanceproduced in Example 7 under excitation by light at 365 nm.

FIG. 15 shows an emission spectrum of the red fluorescent substanceproduced in Example 7 under excitation with a blue LED.

FIG. 16 shows an emission spectrum of the red fluorescent substanceproduced in Example 8 under excitation by light at 365 nm.

FIG. 17 shows an emission spectrum of the red fluorescent substanceproduced in Example 8 under excitation with a blue LED.

FIG. 18 shows an emission spectrum of the red fluorescent substanceproduced in Example 9 under excitation with a blue LED.

FIG. 19 shows an emission spectrum of the red fluorescent substanceproduced in Example 10 under excitation with a blue LED.

FIG. 20 shows comparison among the emission spectra of the fluorescentsubstances produced in Example 3 and Comparative Examples 7 and 8.

FIG. 21 shows a relation between the emission efficiency and theemission wavelength with regard to each of the red fluorescentsubstances produced in Examples 1 to 4, 7 to 10 and Comparative Examples1 to 5.

FIG. 22 shows graphs giving temperature characteristics of the redfluorescent substances produced in Example 6 and Comparative Example 2.

FIG. 23 shows a relation between the emission peak wavelength and theluminance retention rate with regard to each of the red fluorescentsubstances produced in Examples 3, 6 and Comparative Examples 1, 2, 4and 6.

FIG. 24 shows graphs giving temperature characteristics of the redfluorescent substances produced in Example 3 and Comparative Example 4.

FIGS. 25A and B schematically illustrate a light-emitting device moduleproduced in Application Example 101.

FIG. 26 shows a relation between the emission efficiency and the generalcolor rendering index Ra with regard to each of the light-emittingdevice modules produced in Application Examples 101 to 104, 107 to 110and Comparative Application Examples 101 to 105.

FIGS. 27A and B schematically illustrate a light-emitting device moduleproduced in Application Example 201.

FIG. 28 shows a relation between the emission efficiency and the generalcolor rendering index Ra with regard to each of the light-emittingdevice modules produced in Application Examples 201 to 204, 207 to 210and Comparative Application Examples 201 to 205.

FIG. 29 shows a relation between the emission efficiency and the size ofgamut of reproducible colors (NTSC ratio) with regard to each of thelight-emitting device modules produced in Application Examples 301 to304, 307 to 310 and Comparative Application Examples 301 to 305.

FIG. 30 shows transmission spectra of the color filters used in thelight-emitting device of Application Example 301.

FIG. 31 shows a relation between the emission efficiency and the size ofgamut of reproducible colors (NTSC ratio) with regard to each of thelight-emitting device modules produced in Application Examples 401 to404, 407 to 410 and Comparative Application Examples 401 to 405.

DETAILED DESCRIPTION

Embodiments will now be explained with reference to the accompanyingdrawings.

One aspect of the embodiment resides in a red light-emitting fluorescentsubstance represented by the following formula (1):(M_(1-x)EC_(x))_(a)M¹ _(b)AlO_(c)N_(d)  (1).

In the formula (1), M is an element selected from the group consistingof IA group elements, IIA group elements, IIIA group elements, IIIBgroup elements, rare earth elements and IVA group elements; EC is anelement selected from the group consisting of Eu, Ce, Mn, Tb, Yb, Dy,Sm, Tm, Pr, Nd, Pm, Ho, Er, Cr, Sn, Cu, Zn, As, Ag, Cd, Sb, Au, Hg, Tl,Pb, Bi and Fe; M¹ is different from M and is selected from the groupconsisting of tetravalent elements; and x, a, b, c and d are numberssatisfying the conditions of 0<x<0.2, 0.63<a<0.80, 2.1<b<2.63, 0<c≦0.24and 4<d<5, respectively.

This fluorescent substance emits luminescence having a peak in thewavelength range of 620 to 670 nm when excited by light in thewavelength range of 250 to 500 nm.

Red Light-Emitting Fluorescent Substance

The red light-emitting fluorescent substance of the embodimentrepresented by the formula (1):(M_(1-x)EC_(x))_(a)M¹ _(b)AlO_(c)N_(d)  (1).is generally a kind of SiAlON phosphors.

The fluorescent substance according to the embodiment is characterizedby containing oxygen in a very low amount. Oxygen contents ofconventional SiAlON phosphors are relatively so large that the oxygencomponent ratio c in the formula (1) is 0.25 or more. This is because itwas not recognized that a SiAlON phosphor containing a reduced amount ofoxygen has advantageous characteristics. Further, in the conventionalpreparation process, a relatively large amount of Al₂O₃ is used as oneof the starting materials, and some of them are treated in openatmosphere and hence liable to catch or absorb oxygen in air, andconsequently it is very difficult to reduce the oxygen content in thestarting materials. Furthermore, it is also difficult to reduce strictlythe oxygen and moisture contents in a glove box during the preparationprocedure. For these reasons, nobody synthesized the red fluorescentsubstance having the composition according to the present embodiment.

However, the study of the present inventors has revealed that the redlight-emitting fluorescent substance of the formula (1), which containsoxygen in a small amount, has specific characteristics. That is, the redlight-emitting fluorescent substance having low oxygen content gives anemission spectrum in which the peak shifts toward the longer wavelengthside as compared with known fluorescent substances. The reason of thisis presumed as follows. The more oxygen atoms are replaced with nitrogenatoms in the substance matrix, the more the energy level of 4f-orbitalis depressed by the action of the nephelauxetic effect and crystal fieldsplitting. That is because nitrogen atoms form stronger covalent bondsthan oxygen atoms. As a result, the energy difference between 4f-5dlevels decreases and consequently the emission is observed at a longerwavelength. For obtaining this effect, it is necessary for the oxygencomponent ratio c in the formula (1) to satisfy the condition of0<c≦0.24. From the viewpoint of emission wavelength, the oxygencomponent ratio c is preferably as small as possible. However, in viewof easiness in production, the component ratio c is preferably more than0.05, more preferably more than 0.15, further preferably 0.17 or more.Although the component ratio c is up to 0.24 in the present embodiment,it is preferably 0.21 or less because the peak can be further shiftedtoward the longer wavelength side.

The red light-emitting fluorescent substance giving off luminescence ina wavelength region thus shifted toward the longer wavelength side is,for example, combined with a blue LED and a yellow phosphor, so as toimprove color rendition remarkably. In fact, the light-emitting devicecomprising those in combination gives such a large general colorrendering index Ra as to realize a white light-emitting LED devicehaving a Ra value as high as not less than 85 or more than 90.

In the formula (1), M is an element selected from the group consistingof IA group elements, IIA group elements, IIIA group elements, IIIBgroup elements, rare earth elements and IVA group elements.

The metal element M is preferably selected from the group consisting ofIA group (alkali metal) elements such as Li, Na and K; IIA group(alkaline earth metal) elements such as Mg, Ca, Sr and Ba; IIIA groupelements such as B, In and Ga; IIIB group elements such as Y and Sc;rare earth elements such as Gd, La and Lu; and IVA group elements suchas Ge. Most preferably, the metal element M is Sr. The metal element Mmay be either a single element or two or more elements in combination.Although the most preferable metal element M is Sr, a part of Sr may bereplaced with one or more of element M other than Sr. Preferably usablecompounds containing the element M are nitrides, carbides andcyanamides.

The metal element EC functions as an emission center of the fluorescentsubstance. This means that the fluorescent substance of the embodimenthas a crystal structure basically constituted of M¹, Al, O, N and theabove-described element M but that the element M is partly replaced withthe emission center element EC. The EC is an element selected from thegroup consisting of Eu, Ce, Mn, Tb, Yb, Dy, Sm, Tm, Pr, Nd, Pm, Ho, Er,Cr, Sn, Cu, Zn, As, Ag, Cd, Sb, Au, Hg, Tl, Pb, Bi and Fe.

The element M¹ is different from the element M and is selected from thegroup consisting of tetravalent elements. In the SiAlON phosphor of theembodiment, the element M¹ is Si or a substituting element thereof. TheM¹ is selected from tetravalent metal elements, preferably IVA group andIVB group elements such as Si, Ge, Sn, Ti, Zr and Hf. Most preferably,the element M¹ is Si. The metal element M¹ may be either a singleelement or two or more elements in combination.

The fluorescent substance according to the embodiment has specificcomponent ratios. In addition to the aforementioned condition of theoxygen component ratio c, it is also necessary for other componentratios to satisfy the following conditions: 0<x<0.2, 0.63<a<0.80,2.1<b<2.63, 0<c≦0.24 and 4<d<5.

In the fluorescent substance of the embodiment, the component ratio ofM¹ is limited to such a relatively narrow range as 2.1<b<2.63. Thecomponent ratio of M¹ in this range enables to prevent formation ofvariant phase crystals having various luminescent characteristics. Sincehaving the luminescent characteristics different from those of the aimedfluorescent substance, the variant phase crystals may impair colorpurity of the luminescence. It is, therefore, preferred to preventformation of the variant phase crystals. In order to improve the colorpurity, the component ratio of M¹ preferably satisfies the condition of2.1<b<2.5 because the variant phase crystals are further prevented fromforming. Further, the fluorescent substance satisfying this condition isalso excellent in the emission efficiency.

In the fluorescent substance according to the embodiment, the componentratio x of the emission center, namely, the activation concentration,satisfies the condition of 0<x<0.2. The activation concentrations inmany known fluorescent substances are 0.1 or more, and particularlythose in substances emitting luminescence in longer wavelength regionsare generally 0.2 or more. This is because fluorescent substances havinghigh activation concentrations are apt to show emission spectra havingpeaks at wavelengths shifted toward the longer wavelength side. On theother hand, however, their emission efficiencies generally decrease atthe same time. Accordingly, it is difficult for them to improve whitelight-emitting LED devices in both the color rendition or gamut and theemission efficiency. However, it has been found that, if the oxygen andM¹ component ratios are limited as described above according to theembodiment, high color rendition can be realized without increasing theactivation concentration of the emission center element. In other words,the red light-emitting fluorescent substance represented by the formula(1) can be made to give an emission spectrum in a longer wavelengthregion even if the component ratio x is within the range of 0<x<0.2.Further, the emission efficiency thereof is less lowered. The redfluorescent substance according to Patent Document 1 has room forimprovement in temperature characteristics (luminance retention rate ata high temperature) if the Eu concentration is increased, but thesubstance according to the present embodiment can be further improved inthe temperature characteristics because the component ratio x satisfiesthe condition of 0<x<0.2.

The red light-emitting fluorescent substance of the embodiment ischaracterized by comprising the above-described compositions, and isfurther characterized by emitting luminescence having a peak in thewavelength range of 620 to 670 nm under excitation by light in thewavelength range of 250 to 500 nm. In addition, the substance of theembodiment is a kind of SiAlON phosphors and its Eu-activationconcentration is restricted to such a low range as 0<x<0.2, so that itsluminance less depends on the temperature.

Process for Production of Red Light-Emitting Fluorescent Substance

The red light-emitting fluorescent substance of the embodiment can besynthesized from starting materials, such as: nitride, carbide andcyanamide of the element M; nitride, oxide and carbide of the element M¹such as Al and Si; and oxide, nitride and carbonate of the emissioncenter element EC. For example, if the substance containing Sr and Eu asthe element M and the emission center element EC, respectively, is to beproduced, examples of usable materials include Sr₃N₂, AlN, Si₃N₄, Al₂O₃and EuN. The material Sr₃N₂ can be replaced with Ca₃N₂, Ba₃N₂, Sr₂N, SrNor a mixture thereof. Those powdery materials are weighed out and mixedso that the aimed composition can be obtained, and then the powderymixture is fired in a crucible to produce the aimed fluorescentsubstance. In the present embodiment, it is necessary that the oxygencontent in the aimed SiAlON phosphor be restricted to a very low level,and hence it is necessary to reduce the amount of oxygen contained inthe starting materials. In view of that, it is preferred that the amountof Al₂O₃ in the materials be decreased and that of AlN be increased incompensation for the decreased Al₂O₃. Further, in the productionprocedure, it is also necessary to protect as much as possible thestating materials and the firing atmosphere from contamination withimpurities such as oxygen or oxygen-containing compounds. For example,it is preferred to reduce oxygen and moisture concentrations in aglove-box where the powdery materials are weighed out and/or mixed. Itis also preferred to adopt a favorable production process, for example,to use the materials containing oxygen or oxygen-containing impuritiesin as small amounts as possible. The materials may be mixed in a mortarplaced in the glove-box. The crucible is made of, for example, boronnitride, silicon nitride, silicon carbide, carbon, aluminum nitride,SiAlON, aluminum oxide, molybdenum or tungsten.

The red light-emitting fluorescent substance according to the embodimentcan be obtained by firing the mixture of the starting materials for apredetermined time. The firing is preferably carried out under apressure more than the atmospheric pressure. If silicon nitride is usedas one of the materials, the pressure is preferably not less than 5atmospheres so as to prevent the silicon nitride from decomposing at ahigh temperature. The firing temperature is preferably in the range of1500 to 2000° C., more preferably in the range of 1800 to 2000° C. Ifthe temperature is less than 1500° C., it is often difficult to obtainthe aimed fluorescent substance. On the other hand, if the temperatureis more than 2000° C., there is a fear that the materials or the productmay be sublimated. Further, if nitrides are included in the materials,the firing is preferably carried out under N₂ atmosphere because theyare liable to be oxidized. In that case, N₂/H₂ mixed gas atmosphere isalso usable. As described above, the oxygen content in the atmosphereshould be strictly controlled.

The fired product in the form of powder is then subjected toafter-treatment such as washing, if necessary, to obtain a fluorescentsubstance according to the embodiment. If performed, washing can becarried out with acid or pure water.

Light-Emitting Device

A light-emitting device according to the embodiment comprises the abovefluorescent substance and a light-emitting element capable of excitingthe fluorescent substance.

The device according to one aspect of the embodiment comprises: alight-emitting element serving as an excitation source; and acombination of the aforementioned red light-emitting fluorescentsubstance (R) and a yellow light-emitting fluorescent substance (Y) or agreen light-emitting fluorescent substance (G) each of which gives offluminescence under excitation by light given off from the light-emittingelement. Accordingly, the light-emitting device radiates lightsynthesized with emissions from the light-emitting element and the redand yellow or green fluorescent substances.

The light-emitting device according to another aspect of the embodimentcomprises: a light-emitting element serving as an excitation source; anda combination of the above red light-emitting fluorescent substance (R),the above yellow light-emitting fluorescent substance (Y) or greenlight-emitting fluorescent substance (G), and a blue light-emittingfluorescent substance (B) each of which gives off luminescence underexcitation by light given off from the light-emitting element.

The light-emitting element such as LED used in the device is properlyselected according to the fluorescent substances used together.Specifically, it is necessary that light emitted from the light-emittingelement be capable of exciting the fluorescent substances. Further, ifthe device is preferred to radiate white light, the light-emittingelement preferably emits light of such a wavelength that it cancomplement luminescence given off from the fluorescent substances.

In view of the above, if the device comprises the red and yellow orgreen fluorescent substances, the light-emitting element (S1) isgenerally so selected that it emits light in the wavelength range of 250to 500 nm. If the device comprises the red, yellow or green, and bluefluorescent substances, the light-emitting element (S2) is generally soselected that it emits light of 250 to 430 nm.

The light-emitting device according to the embodiment can be in the formof any conventionally known light-emitting device. FIG. 1 is a verticalsectional view schematically illustrating a light-emitting device of theembodiment.

In the light-emitting device shown in FIG. 1, a resin system 100comprises leads 101 and 102 molded as parts of a lead frame and also aresin member 103 formed by unified molding together with the lead frame.The resin member 103 gives a concavity 105 in which the top opening islarger than the bottom. On the inside wall of the concavity, areflective surface 104 is provided.

At the center of the nearly circular bottom of the concavity 105, alight-emitting element 106 is mounted with Ag paste or the like.Examples of the light-emitting element 106 include a light-emittingdiode and a laser diode. The light-emitting element is selected so thatit can emit light in a proper wavelength according to the fluorescentsubstances used together in combination. For example, a semiconductorlight-emitting element such as GaN can be used as the light-emittingelement. The electrodes (not shown) of the light-emitting element 106are connected to the leads 101 and 102 by way of bonding wires 107 and108 made of Au or the like, respectively. The positions of the leads 101and 102 can be adequately modified.

In the concavity 105 of the resin member 103, a phosphor layer 109 isprovided. For forming the phosphor layer 109, a mixture 110 containingthe fluorescent substance of the embodiment can be dispersed orprecipitated in a resin layer 111 made of silicone resin or the like inan amount of 5 to 50 wt %. The fluorescent substance of the embodimentcomprises an oxynitride matrix having high covalency, and hence isgenerally so hydrophobic that it has good compatibility with the resin.Accordingly, scattering at the interface between the resin and thefluorescent substance is prevented enough to improve thelight-extraction efficiency.

The light-emitting element 106 may be of a flip chip type in whichn-type and p-type electrodes are placed on the same plane. This elementcan avoid troubles concerning the wires, such as disconnection ordislocation of the wires and light-absorption by the wires. In thatcase, therefore, a semiconductor light-emitting device excellent both inreliability and in luminance can be obtained. Further, it is alsopossible to employ an n-type substrate in the light-emitting element 106so as to produce a light-emitting device constituted as described below.In that device, an n-type electrode is formed on the back surface of then-type substrate while a p-type electrode is formed on the top surfaceof the semiconductor layer on the substrate. One of the n-type andp-type electrodes is mounted on one of the leads, and the otherelectrode is connected to the other lead by way of a wire. The size ofthe light-emitting element 106 and the dimension and shape of theconcavity 105 can be properly changed.

The light-emitting device according to the embodiment is not restrictedto the package cup-type shown in FIG. 1, and can be freely applied toany type of devices. For example, even if the fluorescent substanceaccording to the embodiment is used in a shell-type or surface-mounttype light-emitting device, the same effect can be obtained.

Meanwhile, a light-emitting device module according to the embodimentcomprises a plural number of the afore-mentioned light-emitting devicesarranged on a substrate. Any of the above light-emitting devices, whichcomprise the fluorescent substance of the embodiment, can be freelyselected to be used in the module. For example, the shell-type devicedescribed above is one of those preferably employed in the module.Specifically, the light-emitting device module comprises a plural numberof any of the following light-emitting devices:

(1) a light-emitting device having a laminate structure produced by thesteps of: providing, on a substrate, a light-emitting element (S1)giving off light in the wavelength range of 250 to 500 nm; formingthereover a dome with transparent resin; coating the dome with the abovered fluorescent substance (R) dispersed in transparent resin; andapplying thereon a yellow or green light-emitting fluorescent substance(Y) or (G) dispersed in transparent resin; and

(2) a light-emitting device having a laminate structure produced by thesteps of: providing, on a substrate, a light-emitting element (S2)giving off light in the wavelength range of 250 to 430 nm; formingthereover a dome with transparent resin; coating the dome with the abovered fluorescent substance (R) dispersed in transparent resin; applyingthereon a yellow or green fluorescent substance (Y) or (G) dispersed intransparent resin; and further applying thereon a blue light-emittingfluorescent substance (B) dispersed in transparent resin.

There is no particular restriction on materials of the substrate, andhence it can be freely selected from known materials according to theaim. Examples of the materials include glass, silicon, semiconductorsand resins. The surface of the substrate may be subjected to variousmodifications according to necessity. For example, wiring or isolationstructures for the light-emitting devices can be laid on the surface.Further, in order to improve heat-dissipating, a heat-sinking layer canbe formed thereon. The substrate in itself may be a heat-sinkingsubstrate excellent in thermal conductivity.

The yellow fluorescent substance gives off luminescence having a peak inthe wavelength range of 540 to 580 nm when excited by light emitted fromthe light-emitting element (S1) or (S2). The yellow phosphor selectedfrom the group consisting of YAG phosphor, (Sr,Ca,Ba,Eu)₂SiO₄,(Sr,Ca,Ba,Eu)₃SiO₅, (CaEu)Ga₂S₄, and α-SiAlON phosphor is preferred. TheYAG phosphor is yellow phosphor containing yttrium, aluminum and ceriumwhich has garnet structure. α-SiAlON emitting yellow fluorescence has anoverall composition given by the formula:M_(m/v)S^(12−(m+n))Al_(m+n)O_(n)N_(16−n).where M is the modifying cations such as Li, Mg, Ca, Sr, Y, and rareearth (excluding La, Ce, Pr, and Eu), and v is the valence of the cationM. The crystal structure of α-SiAlON is derived from α-Si₃N₄ by partialreplacement of Si⁴⁺ by Al³⁺ and N³⁻ by O²⁻ simultaneously, as well asstabilized by trapping cation M into the interstices of the(Si,Al)—(O,N)₄ network. The blue fluorescent substance gives offluminescence having a peak in the wavelength range of 400 to 490 nm whenexcited by light emitted from the light-emitting element (S1) or (S2).

The green fluorescent substance gives off luminescence having a peak inthe wavelength range of 490 to 540 nm when excited by light emitted fromthe light-emitting element (S1) or (S2), and the blue fluorescentsubstance gives off luminescence having a peak in the wavelength rangeof 400 to 490 nm when excited by light emitted from the light-emittingelement (S1) or (S2)

The light-emitting devices are regularly or irregularly arranged on thesubstrate to form a light-emitting device module. Since having excellenttemperature characteristics, the fluorescent substance of the embodimentis hardly affected by heat generated in operation. Accordingly, thedevices comprising the fluorescent substances can be arranged so denselythat the interval among them can be shortened. For example, theaforementioned shell-type devices seem to be circles or ellipses whenseen from above, and they can be placed in such an arrangement assatisfies the condition of (d/a)≦5 in which “a” and “d” are the majoraxis length of the ellipses and the shortest distance among them,respectively. The “major axis length” here means the longest diameter ofthe horizontal section of each light-emitting device. In other words, ifeach light-emitting device has a circular or elliptical horizontalsection, it means its diameter or its major axis length, respectively.If necessary, the light-emitting devices can have sections in anyshapes, such as rectangles, polygons or lines. In that case, theinterval among them cannot be uniformly regulated. Even so, however, theinterval among them can be shortened enough to enhance the luminance ofthe whole light-emitting device module. That is because the fluorescentsubstance of the embodiment is so excellent in temperaturecharacteristics that its luminescence is hardly affected by heatgenerated by the adjacent light-emitting devices in operation. From theviewpoint of easiness in production, the (d/a) cannot be too small andis generally 1≦(d/a).

It is indispensable to employ the red light-emitting fluorescentsubstance of the embodiment in a light-emitting device or alight-emitting device module according to the embodiment. However, asfor the yellow light-emitting fluorescent substance (Y), the greenlight-emitting fluorescent substance (G) and the blue light-emittingfluorescent substance (B), there is no particular restriction. The redfluorescent substance (R) of the embodiment has such excellenttemperature characteristics that it is hardly affected by temperaturechange. In order to utilize this advantage to the utmost, both theyellow or green fluorescent substance (Y) or (G) and the blue one (B)are preferably excellent in temperature characteristics, too. Ifcomprising those preferred fluorescent substances, the light-emittingdevice or module gives off light less changed in color even when thetemperature is changed. That is not only because the red fluorescentsubstance gives off luminescence less changed in intensity but alsobecause the other fluorescent substances give off luminescence lesschanged in intensity, too.

Examples of the preferred blue fluorescent substance excellent intemperature characteristics include (Ba,Eu)MgAl₁₀O₁₇,(Sr,Ca,Ba,Eu)₁₀(PO₄)₅Cl₂ and (Sr,Eu)Si₉Al₁₉ON₃₁.

The embodiment is further explained by the following examples, which byno means restrict the embodiment.

Example 1

As the starting materials, Sr₃N₂, EuN, Si₃N₄ and AlN in the amounts of2.443 g, 0.465 g, 4.583 g and 1.721 g, respectively, were weighed outand dry-mixed in an agate mortar in a vacuum glove box. The mixture wasplaced in a BN crucible and then fired at 1850° C. for 4 hours under 7.5atm of N₂ atmosphere, to synthesize a red light-emitting fluorescentsubstance (R1).

The substance (R1) after firing was in the form of orange powder, andemitted red luminescence when exited with black light. FIGS. 2, 3 andTable 1 show an XRD profile, an emission spectrum under excitation bylight at 458 nm, and a result of composition analysis (in terms of molarratio provided that the Al component is regarded as 1.00), respectively,of the obtained red fluorescent substance. In FIG. 3, the band having apeak at 458 nm is attributed to reflection of the excitation light. As aresult, the fluorescent substance of Example 1 was found to show anemission spectrum of a single band having a peak at 640 nm.

Example 2

The procedure of Example 1 was repeated except that only the firingatmosphere was changed, to synthesize a red light-emitting fluorescentsubstance (R2).

The substance (R2) after firing was in the form of orange powder, andemitted red luminescence when exited with black light. FIG. 4 and Table1 show an emission spectrum under excitation by light at 460 nm and aresult of composition analysis (in terms of molar ratio provided thatthe Al component is regarded as 1.00), respectively, of the obtained redfluorescent substance. In FIG. 4, the band having a peak at 460 nm isattributed to reflection of the excitation light. As a result, thefluorescent substance of Example 2 was found to show an emissionspectrum of a single band having a peak at 640 nm.

Example 3

The procedure of Example 1 was repeated except that only the firing timewas changed into 2 hours, to synthesize a red light-emitting fluorescentsubstance (R3).

The substance (R3) after firing was in the form of orange powder, andemitted red luminescence when exited with black light. FIGS. 5, 6, 7 andTable 1 show an XRD profile, emission spectra under excitation by lightat 365 nm and 457 nm, and a result of composition analysis (in terms ofmolar ratio provided that the Al component is regarded as 1.00),respectively, of the obtained red fluorescent substance. In FIG. 7, theband having a peak at 457 nm is attributed to reflection of theexcitation light. As a result, the fluorescent substance of Example 3was found to show an emission spectrum of a single band having a peak at638 nm.

Example 4

The procedure of Example 3 was repeated except that only the firingatmosphere was changed, to synthesize a red light-emitting fluorescentsubstance (R4).

The substance (R4) after firing was in the form of orange powder, andemitted red luminescence when exited with black light. FIGS. 8, 9 andTable 1 show emission spectra under excitation by light at 365 nm and461 nm and a result of composition analysis (in terms of molar ratioprovided that the Al component is regarded as 1.00), respectively, ofthe obtained red fluorescent substance. In FIG. 9, the band having apeak at 461 nm is attributed to reflection of the excitation light. As aresult, the fluorescent substance of Example 4 was found to show anemission spectrum of a single band having a peak at 640 nm.

Example 5

As the starting materials, Sr₃N₂, EuN, Si₃N₄ and AlN in the amounts of2.660 g, 0.093 g, 4.583 g and 1.721 g, respectively, were weighed outand dry-mixed in an agate mortar in a vacuum glove box. The mixture wasplaced in a BN crucible and then fired at 1850° C. for 3 hours under 7.5atm of N₂ atmosphere, to synthesize a red light-emitting fluorescentsubstance (R5).

The substance (R5) after firing was in the form of orange powder, andemitted red luminescence when exited with black light. FIGS. 10, 11 andTable 1 show emission spectra under excitation by light at 365 nm and457 nm and a result of composition analysis (in terms of molar ratioprovided that the Al component is regarded as 1.00), respectively, ofthe obtained red fluorescent substance. In FIG. 11, the band having apeak at 457 nm is attributed to reflection of the excitation light. As aresult, the fluorescent substance of Example 5 was found to show anemission spectrum of a single band having a peak at 620 nm.

Example 6

The procedure of Example 5 was repeated except that only the firingatmosphere was changed, to synthesize a red light-emitting fluorescentsubstance (R6).

The substance (R6) after firing was in the form of orange powder, andemitted red luminescence when exited with black light. FIGS. 12, 13 andTable 1 show emission spectra under excitation by light at 365 nm and457 nm and a result of composition analysis (in terms of molar ratioprovided that the Al component is regarded as 1.00), respectively, ofthe obtained red fluorescent substance. In FIG. 13, the band having apeak at 457 nm is attributed to reflection of the excitation light. As aresult, the fluorescent substance of Example 6 was found to show anemission spectrum of a single band having a peak at 622 nm.

Example 7

As the starting materials, Sr₃N₂, EuN, Si₃N₄ and AlN in the amounts of2.525 g, 0.325 g, 4.583 g and 1.721 g, respectively, were weighed outand dry-mixed in an agate mortar in a vacuum glove box. The mixture wasplaced in a BN crucible and then fired at 1850° C. for 3 hours under 7.5atm of N₂ atmosphere, to synthesize a red light-emitting fluorescentsubstance (R7).

The substance (R7) after firing was in the form of orange powder, andemitted red luminescence when exited with black light. FIGS. 14, 15 andTable 1 show emission spectra under excitation by light at 365 nm and457 nm and a result of composition analysis (in terms of molar ratioprovided that the Al component is regarded as 1.00), respectively, ofthe obtained red fluorescent substance. In FIG. 15, the band having apeak at 457 nm is attributed to reflection of the excitation light. As aresult, the fluorescent substance of Example 7 was found to show anemission spectrum of a single band having a peak at 636 nm.

Example 8

The procedure of Example 7 was repeated except that only the firingatmosphere was changed, to synthesize a red light-emitting fluorescentsubstance (R8).

The substance (R8) after firing was in the form of orange powder, andemitted red luminescence when exited with black light. FIGS. 16, 17 andTable 1 show emission spectra under excitation by light at 365 nm and457 nm and a result of composition analysis (in terms of molar ratioprovided that the Al component is regarded as 1.00), respectively, ofthe obtained red fluorescent substance. In FIG. 17, the band having apeak at 457 nm is attributed to reflection of the excitation light. As aresult, the fluorescent substance of Example 8 was found to show anemission spectrum of a single band having a peak at 635 nm.

Example 9

As the starting materials, Sr₃N₂, EuN, Si₃N₄, Al₂O₃ and AlN in theamounts of 2.321 g, 0.441 g, 5.075 g, 0.119 g and 1.195 g, respectively,were weighed out and dry-mixed in an agate mortar in a vacuum glove box.The mixture was placed in a BN crucible and then fired at 1850° C. for 1hour under 7.5 atm of N₂ atmosphere, to synthesize a red light-emittingfluorescent substance (R9).

The substance (R9) after firing was in the form of orange powder, andemitted red luminescence when exited with black light. FIG. 18 and Table1 show an emission spectrum under excitation by light at 458 nm and aresult of composition analysis (in terms of molar ratio provided thatthe Al component is regarded as 1.00), respectively, of the obtained redfluorescent substance. In FIG. 18, the band having a peak at 458 nm isattributed to reflection of the excitation light. As a result, thefluorescent substance of Example 9 was found to show an emissionspectrum of a single band having a peak at 629 nm.

Example 10

The procedure of Example 9 was repeated except that only the firingatmosphere was changed, to synthesize a red light-emitting fluorescentsubstance (R10).

The substance (R10) after firing was in the form of orange powder, andemitted red luminescence when exited with black light. FIG. 19 and Table1 show an emission spectrum under excitation by light at 461 nm and aresult of composition analysis (in terms of molar ratio provided thatthe Al component is regarded as 1.00), respectively, of the obtained redfluorescent substance. In FIG. 19, the band having a peak at 461 nm isattributed to reflection of the excitation light. As a result, thefluorescent substance of Example 10 was found to show an emissionspectrum of a single band having a peak at 629 nm.

Comparative Example 1 Eu 10%

The procedure of Example 1 was repeated except that Sr₃N₂, EuN, Si₃N₄,Al₂O₃ and AlN were used in the amounts of 2.443 g, 0.465 g, 4.583 g,0.476 g and 1.339 g, respectively, to synthesize a fluorescentsubstance. The obtained substance was combined with a blue LED and ayellow phosphor YAG to produce a white LED, which was found to have acolor temperature of 2800 K and a Ra value of 73.

Comparative Example 2 Eu 20%

The procedure of Example 1 was repeated except that Sr₃N₂, EuN, Si₃N₄,Al₂O₃ and AlN were used in the amounts of 2.172 g, 0.929 g, 4.583 g,0.476 g and 1.339 g, respectively, to synthesize a fluorescentsubstance.

Comparative Example 3 Eu 40%

The procedure of Example 1 was repeated except that Sr₃N₂, EuN, Si₃N₄,Al₂O₃ and AlN were used in the amounts of 1.629 g, 1.859 g, 4.583 g,0.476 g and 1.339 g, respectively, to synthesize a fluorescentsubstance.

Comparative Example 4 Eu 50%

The procedure of Example 1 was repeated except that Sr₃N₂, EuN, Si₃N₄,Al₂O₃ and AlN were used in the amounts of 1.357 g, 2.324 g, 4.583 g,0.476 g and 1.339 g, respectively, to synthesize a fluorescentsubstance.

Comparative Example 5 Eu 80%

The procedure of Example 1 was repeated except that Sr₃N₂, EuN, Si₃N₄,Al₂O₃ and AlN were used in the amounts of 0.543 g, 3.718 g, 4.583 g,0.476 g and 1.339 g, respectively, to synthesize a fluorescentsubstance.

Comparative Example 6 Eu 15%

The procedure of Example 1 was repeated except that Sr₃N₂, EuN, Si₃N₄,Al₂O₃ and AlN were used in the amounts of 2.308 g, 0.697 g, 4.583 g,0.476 g and 1.339 g, respectively, to synthesize a fluorescentsubstance.

Comparative Example 7

The procedure of Example 1 was repeated except that Sr₃N₂, EuN, Si₃N₄,Al₂O₃ and AlN were used in the amounts of 2.172 g, 0.929 g, 4.747 g,0.357 g and 1.291 g, respectively, to synthesize a fluorescentsubstance.

Comparative Example 8

The procedure of Example 1 was repeated except that Sr₃N₂, EuN, Si₃N₄,Al₂O₃ and AlN were used in the amounts of 2.172 g, 0.929 g, 4.420 g,0.595 g and 1.387 g, respectively, to synthesize a fluorescentsubstance.

FIG. 20 shows emission spectra of the fluorescent substances prepared inExample 3 and Comparative Examples 7 and 8. In comparison with thespectrum of Example 3, the spectra of Comparative Examples 7 and 8 havesmall peaks (around 500 nm) on the shorter wavelength side of the mainpeaks. Those small peaks are presumed to be attributed to variant phasecrystals, which are different from the aimed fluorescent substances. Ascompared with the spectra of Comparative Examples 7 and 8, the spectrumof Example 3 is shifted toward the longer wavelength side and does nothave the shorter-side peak. Accordingly, it indicates that variant phasecrystals were less formed in Example 3. This is presumed to be becausethe component ratio of Si (element M¹) satisfies the condition of2.1<b<2.63.

In Comparative Example 7, the amounts of the starting materials were sodesigned that the component ratio b might be 2.64. However, as a result,a green fluorescent substance represented by Sr₃Si₁₃Al₃O₂N₂₁:Eu, whichhas a high Si component, was produced in a considerable amount. It seemsto be difficult to synthesize a red light-emitting fluorescent substancehaving a component ratio b of 2.64 or more. Even if it is attempted toproduce a crystal of that composition, various variant phase crystalswill be formed in considerable amounts.

In Comparative Example 8, the amounts of the starting materials were sodesigned that the component ratio b might be 2.08. However, as a result,blue and green light-emitting fluorescent substances were produced inconsiderable amounts, as compared with production of the red fluorescentsubstance in Example 2. Accordingly, it seems to be also difficult tosynthesize a red light-emitting fluorescent substance having a componentratio b of 2.1.

The fluorescent substances of Examples and Comparative Examples weresubjected to composition analysis, and the results were as set forth inTable 1. The composition ratios in Table 1 were normalized by regardingthe content of Al as 1.00.

The composition of oxynitride fluorescent substance can be analyzed inany known manner, for example, in the following manner.

The contents of M, M¹, Al and EC can be measured by, for example,inductively coupled plasma atomic emission spectroscopic analysis (oftenreferred to as “ICP analysis”). Specifically, the sample of oxynitridefluorescent substance is weighed out in a platinum crucible and thendecomposed by alkali fusion. After an internal standard element Y isadded, the decomposed sample is dissolved to prepare a sample solution,which is subsequently subjected to ICP analysis. With respect to M, M¹and EC, the analysis can be carried out by means of, for example, an ICPemission spectrometry (SPS-4000 [trademark], manufactured by SII NanoTechnology Inc.).

The contents of O and N can be measured, for example, by the inert gasfusion method. Specifically, the sample of oxynitride fluorescentsubstance is heated to melt in a graphite crucible, and O atomscontained in the sample are converted into CO with inert gas transfer.The CO is further oxidized into CO₂, which is then measured by IRabsorption spectroscopy to determine the content of O. After the CO₂ isremoved from the sample, the content of N is measured by the heatconduction method. The measurement can be carried out by means of, forexample, an oxygen, nitrogen-hydrogen analyzer (TC-600 [trademark],manufactured by LECO corporation (US)). The content of C was measured bya carbon/sulfur analyzer (CS-444LS [trademark], manufactured by LECOcorporation (US)) by means of high frequency combustion-IR absorptionspectroscopy.

TABLE 1 Results of composition analysis by ICP (normalized by regardingthe content of Al as 1.00) Sr Eu Al Si O N C Ex. 1 0.61 0.07 1.00 2.460.21 4.39 0.02 Ex. 2 0.64 0.07 1.00 2.63 0.21 4.72 0.02 Ex. 3 0.59 0.071.00 2.35 0.20 4.56 0.02 Ex. 4 0.58 0.07 1.00 2.39 0.18 4.56 0.02 Ex. 50.63 0.01 1.00 2.42 0.17 4.56 0.02 Ex. 6 0.62 0.01 1.00 2.40 0.17 4.430.03 Ex. 7 0.62 0.05 1.00 2.46 0.19 4.55 0.03 Ex. 8 0.60 0.05 1.00 2.410.17 4.43 0.02 Ex. 9 0.57 0.06 1.00 2.35 0.24 4.27 0.03 Ex. 10 0.57 0.061.00 2.38 0.23 4.31 0.03 Com. 1 0.60 0.07 1.00 2.26 0.43 4.19 0.01 Com.3 0.42 0.28 1.00 2.32 0.48 4.30 0.01 Com. 4 0.34 0.34 1.00 2.29 0.484.14 0.01 Com. 5 0.14 0.57 1.00 2.35 0.51 4.25 0.01

The substances of Examples contained oxygen in decreased amounts, ascompared with those of Comparative Examples. One of the reasons for thisis that oxygen contained in the starting materials was reduced in eachExample. Specifically, the amount of Al₂O₃ in the materials wasdecreased and that of AlN was increased in compensation for thedecreased Al₂O₃, and further the starting materials were so selectedthat they might contain impurities in low amounts.

Another reason is because oxygen and moisture concentrations werereduced in the glove-box, where the materials were weighed out andmixed. Specifically, the materials containing decreased amounts ofoxygen were weighed out and mixed in the vacuum glove box in whoseatmosphere oxygen was strictly controlled.

In Examples 1 to 8, the materials included no oxide and the firing wascarried out in N₂ atmosphere, and thereby oxygen was intentionallyavoided. Nevertheless, since it was impossible to remove oxygencompletely from the materials and the atmosphere, the resultantfluorescent substances still contained oxygen. However, they had suchsmall oxygen contents as had never been realized before. That is becauseof the production process according to the embodiment. In the productionprocess of the embodiment as contrasted with that of known SiAlONphosphors, the amount of Al₂O₃ in the starting materials was decreasedand that of AlN was increased in compensation for the decreased Al₂O₃,and the starting materials were so purified that they might containoxygen in low amounts. Further, in prior arts, some of the materialswere treated out of a glove box. In contrast, in the process of theembodiment, all the materials were treated in the glove box in whoseatmosphere oxygen concentration was strictly controlled to be reduced.

With respect to the red fluorescent substances of Examples andComparative Examples, Table 2 shows their chromaticity coordinates (x,y) in the CIE1931 chromaticity diagram.

TABLE 2 chromaticity coordinate (CIE1931) Cx Cy Ex. 1 0.590 0.358 Ex. 20.586 0.349 Ex. 3 0.608 0.375 Ex. 4 0.610 0.372 Ex. 5 0.544 0.420 Ex. 60.546 0.419 Ex. 7 0.591 0.368 Ex. 8 0.591 0.370 Ex. 9 0.560 0.374 Ex. 100.555 0.368 Com. 1 0.512 0.431 Com. 2 0.538 0.417 Com. 3 0.565 0.404Com. 4 0.565 0.406 Com. 5 0.558 0.396 Com. 7 0.540 0.440 Com. 8 0.5100.420Evaluation of Emission Efficiency

With respect to the fluorescent substance of each Example andComparative Example, Table 3 shows the emission peak wavelength (nm) andthe emission efficiency (in terms of relative value provided that theefficiency in Comparative Example 1 is regarded as 1).

TABLE 3 Peak wavelength Emission efficiency (nm) (relative value) Ex. 1638 0.74 Ex. 2 640 0.71 Ex. 3 638 0.84 Ex. 4 640 0.81 Ex. 5 620 0.79 Ex.6 622 0.78 Ex. 7 637 0.9 Ex. 8 635 0.86 Ex. 9 629 0.79 Ex. 10 629 0.78Com. 1 610 1 Com. 2 617 0.9 Com. 3 623 0.67 Com. 4 626 0.62 Com. 5 6350.29

FIG. 21 shows a relation between the emission efficiency and theemission peak wavelength with regard to each of the fluorescentsubstances produced in Examples 1 to 4, 7 to 10 and Comparative Examples1 to 5. In FIG. 21, the emission efficiency is plotted on the verticalaxis in terms of relative value provided that the efficiency of thesubstance produced in Comparative Example 1 is regarded as 1.0. FIG. 21indicates that the emission efficiencies of Comparative Examplesdecrease according as the emission peak wavelengths become longer. Onthe other hand, as compared with Comparative Examples, the substances ofExamples have high efficiencies even if their emission peaks are locatedat longer wavelengths. The substances of Comparative Examples contain Euin relatively high concentrations, and thereby they give offluminescence in longer wavelength regions. However, if Eu is containedin a high concentration, the energy is more likely to be transferredamong the Eu atoms to lower the emission efficiency (i.e., concentrationquenching). In contrast, the Eu concentration in the fluorescentsubstance of the embodiment is kept low but the oxygen/nitrogen ratio isreduced so as to shift the emission wavelength toward the longerwavelength side. Accordingly, even if emitting luminescence in a longerwavelength region, the substance according to the embodiment does notundergo the concentration quenching and hence can keep high emissionefficiency. Thus, the oxygen contents were reduced as compared withknown fluorescent substances, and thereby it succeeded to obtainfluorescent substances that give off luminescence in longer wavelengthregions with high efficiencies.

Evaluation of Temperature Characteristics

The red powdery substances of Example 6 and Comparative Example 2 wereexcited while they were being heated with a heater from room temperatureto 200° C., to measure the change of the emission spectra. The lightsource used for excitation was a LED giving off light having a peak at458 nm. The results were shown in FIG. 22, which indicates temperaturedependence of the peak intensities in the emission spectra. The relativeintensity plotted on the y-axis in FIG. 22 was normalized under thecondition that the emission intensity of each fluorescent substance atroom temperature was regarded as 1.00.

FIG. 22 indicates that the red fluorescent substance of Example 6 haslarger luminance retention rates at high temperatures than that ofComparative Example 2, which has relatively good temperaturecharacteristics.

FIG. 23 shows a relation between the emission peak wavelength and theluminance retention rate at 150° C. with regard to each of the redfluorescent substances produced in Examples 3, 6 and ComparativeExamples 1, 2, 4 and 6. The luminance retention rate at 150° C. heremeans a relative emission intensity at 150° C. under the condition thatthe emission intensity at room temperature is regarded as 1.00. As shownin FIG. 23, the luminance retention rates of Comparative Examples at ahigh temperature decrease according as the emission peak wavelengthsbecome longer. On the other hand, however, the substances according tothe embodiment keep higher luminance retention rates than those ofComparative Examples at the same emission peak wavelengths. Further, itshould be noted that the substances of Example 6 and Comparative Example2 show emission peaks at 622 nm and 617 nm, respectively. That is,although the substance of Example 6 has a longer emission peakwavelength than that of Comparative Example 2, the former keeps a higherluminance retention rate than the latter.

FIG. 24 shows graphs giving temperature characteristics of the redfluorescent substances produced in Example 3 and Comparative Example 4.In prior arts, known fluorescent substances are liable to have lowerluminance retention rates at high temperatures according as the emissionwavelengths become longer. However, as shown in FIG. 24, the substanceof the embodiment produced in Example 3 has a longer emission wavelengthbut better temperature characteristics than the substance of ComparativeExample 4.

The present embodiment thus enables to produce a fluorescent substancegiving luminescence in a longer wavelength region but having largerluminance retention rates at high temperatures. Since often used at hightemperatures, a white light-emitting LED device is required to giveemission intensity strong enough to ensure high emission efficiency athigh temperatures. Further, the white LED device is also wanted to keepluminance retention rates large enough to prevent the white LED fromcolor discrepancies at high temperatures. From those viewpoints, the redfluorescent substance of the embodiment is suitable for a whitelight-emitting LED device.

Application to Device Illumination Application Examples 101 to 104, 107to 110 and Comparative Application Examples 101 to 105 Under Excitationwith a Blue Light-Emitting LED Element

A light-emitting device module of Application Example 101 was producedby use of the fluorescent substance synthesized in Example 1. FIG. 25Ais a conceptual sketch showing the light-emitting device module ofApplication Example 101. This module comprised a heat-sinking substrate2502 and plural shell-type light-emitting devices 2500 arranged thereon.Each shell-type light-emitting device had a structure shown in FIG. 25B.The light-emitting device module was produced in the following manner.First, sixteen LEDs 2501 emitting light having a peak at 455 nm wereprepared, and they were placed and soldered on the heat-sinkingsubstrate 2502 in such an arrangement that the center-to-center intervalamong them might be 6 mm. Subsequently, each LED soldered on thesubstrate was connected to electrodes by way of gold wires 2503. EachLED was then domed with transparent resin 2504, and the dome was coatedwith a layer of transparent resin 2505 containing the red fluorescentsubstance of Example 1. Further, another layer of transparent resin 2506and still another layer of transparent resin 2507 containing a yellowfluorescent substance giving off luminescence having a peak at 565 nmwere stacked thereon in order, to produce a light-emitting devicemodule. Each device seemed to be a circle when seen from above, and itsdiameter was 2.8 mm.

The procedure of Application Example 101 was repeated except for usingeach of the fluorescent substances synthesized in Examples 2 to 4, 7 to10 and Comparative Examples 1 to 5, to produce each light-emittingdevice module of Application Examples 102 to 104, 107 to 110 andComparative Application Examples 101 to 105.

As for each module of Application Examples 101 to 104, 107 to 110 andComparative Application Examples 101 to 105, Table 4 and FIG. 26 showthe emission efficiency (Im/W) and the general color rendering index Ra,respectively.

TABLE 4 general color Emission efficiency rendering index: Ra (lm/W) Ap.Ex. 101 90.1 55 Ap. Ex. 102 91.1 52 Ap. Ex. 103 89.2 61 Ap. Ex. 104 89.959 Ap. Ex. 107 89.1 64 Ap. Ex. 108 89.0 63 Ap. Ex. 109 86.6 61 Ap. Ex.110 86.7 61 Com. Ap. 101 75.6 70 Com. Ap. 102 81.5 65 Com. Ap. 103 84.652 Com. Ap. 104 84.8 50 Com. Ap. 105 88.4 26

The above results indicate that it was difficult for the modules ofComparative Application Examples 101 to 105, which adopted conventionalfluorescent substances, to realize both high emission efficiencies andhigh color rendition. On the other hand, however, the results alsoindicate that the modules of Application Examples 101 to 104 and 107 to110 according to the embodiment realized both high emission efficienciesand high color rendition, as compared with those of ComparativeApplication Examples.

Application Examples 201 to 204, 207 to 210 and Comparative ApplicationExamples 201 to 205 Under Excitation with a UV Light-Emitting LedElement

A light-emitting device module of Application Example 201 was producedby use of the fluorescent substance synthesized in Example 1. FIG. 27Ais a conceptual sketch showing the light-emitting device module ofApplication Example 201. This module comprised a heat-sinking substrate2702 and plural shell-type light-emitting devices 2700 arranged thereon.Each shell-type light-emitting device had a structure shown in FIG. 27B.The light-emitting device module was produced in the following manner.First, sixteen LEDs 2701 giving off light having a peak at 390 nm wereprepared, and they were placed and soldered on the heat-sinkingsubstrate 2702 in such an arrangement that the center-to-center intervalamong them might be 6 mm. Subsequently, each LED soldered on thesubstrate was connected to electrodes by way of gold wires 2703. EachLED was then domed with transparent resin 2704, and the dome was coatedwith a layer of transparent resin 2705 containing the red fluorescentsubstance of Example 1. Further, another layer of transparent resin2706, still another layer of transparent resin 2707 containing a yellowfluorescent substance giving off luminescence having a peak at 565 nm,yet another layer of transparent resin 2708 and still yet another layerof transparent resin 2709 containing a blue fluorescent substance givingoff luminescence having a peak at 452 nm were stacked thereon in order,to produce a light-emitting device. Each device seemed to be a circlewhen seen from above, and its diameter was 3.0 mm.

The procedure of Application Example 201 was repeated except for usingeach of the fluorescent substances synthesized in Examples 2 to 4, 7 to10 and Comparative Examples 1 to 5, to produce each light-emittingdevice module of Application Examples 202 to 204, 207 to 210 andComparative Application Examples 201 to 205.

As for each module of Application Examples 201 to 204, 207 to 210 andComparative Application Examples 201 to 205, Table 5 and FIG. 28 showthe emission efficiency (Im/W) and the general color rendering index Ra,respectively.

TABLE 5 general color Emission efficiency rendering index: Ra (lm/W) Ap.Ex. 201 91.0 35 Ap. Ex. 202 92.1 33 Ap. Ex. 203 90.2 39 Ap. Ex. 204 90.838 Ap. Ex. 207 90.1 41 Ap. Ex. 208 89.9 41 Ap. Ex. 209 87.2 39 Ap. Ex.210 87.6 39 Com. Ap. 201 77.5 49 Com. Ap. 202 82.4 44 Com. Ap. 203 85.535 Com. Ap. 204 85.7 34 Com. Ap. 205 89.3 17

The above results indicate that it was difficult for the modules ofComparative Application Examples 201 to 205, which adopted conventionalfluorescent substances, to realize both high emission efficiencies andhigh color rendition. On the other hand, however, the results alsoindicate that the modules of Application Examples 201 to 204 and 207 to210 according to the embodiment realized both high emission efficienciesand high color rendition, as compared with those of ComparativeApplication Examples.

Application to Backlight Application Examples 301 to 304, 307 to 310 andComparative Application Examples 301 to 305 Under Excitation with a BlueLight-Emitting LED Element

A light-emitting device module of Application Example 301 was producedby use of the fluorescent substance synthesized in Example 1. Theprocedure of Application Example 101 was repeated except that thefluorescent substance contained in the transparent resin layer 2507 waschanged into the green one giving off luminescence having a peak at 520nm, to produce the module of Application Example 301.

The procedure of Application Example 301 was repeated except for usingeach of the fluorescent substances synthesized in Examples 2 to 4, 7 to10 and Comparative Examples 1 to 5, to produce each light-emittingdevice module of Application Examples 302 to 304, 307 to 310 andComparative Application Examples 301 to 305.

As for each module of Application Examples 301 to 304, 307 to 310 andComparative Application Examples 301 to 305, Table 6 and FIG. 29 showthe emission efficiency and the NTSC ratio (i.e., value in the u′-v′chromaticity coordinate system on the CIE1976 chromaticity diagram)measured through a diffuser and color filters, whose transmissionspectra are shown in FIG. 30.

TABLE 6 Emission efficiency (lm/W) NTSC ratio (%) Ap. Ex. 301 47.4 95.9Ap. Ex. 302 45.2 96.7 Ap. Ex. 303 52.5 95.4 Ap. Ex. 304 50.7 95.9 Ap.Ex. 307 54.7 95.3 Ap. Ex. 308 54.5 95.2 Ap. Ex. 309 54.1 93.5 Ap. Ex.310 53.3 93.8 Com. Ap. 301 65.7 89.3 Com. Ap. 302 61.0 90.2 Com. Ap. 30349.3 91.6 Com. Ap. 304 47.0 91.7 Com. Ap. 305 24.7 93.1

The above results indicate that it was difficult for the modules ofComparative Application Examples 301 to 305, which adopted conventionalfluorescent substances, to realize both high emission efficiencies andlarge NTSC ratios. On the other hand, however, the results also indicatethat the modules of Application Examples 301 to 304 and 307 to 310according to the embodiment realized both high emission efficiencies andlarge NTSC ratios, as compared with those of Comparative ApplicationExamples.

Application Examples 401 to 404, 407 to 410 and Comparative ApplicationExamples 401 to 405 Under Excitation with a UV Light-Emitting LEDElement

A light-emitting device module of Application Example 401 was producedby use of the fluorescent substance synthesized in Example 1. Theprocedure of Application Example 201 was repeated except that thefluorescent substance contained in the transparent resin layer 2707 waschanged into the green one giving off luminescence having a peak at 520nm, to produce the module of Application Example 401.

The procedure of Application Example 401 was repeated except for usingeach of the fluorescent substances synthesized in Examples 2 to 4, 7 to10 and Comparative Examples 1 to 5, to produce each light-emittingdevice module of Application Examples 402 to 404, 407 to 410 andComparative Application Examples 401 to 405.

As for each module of Application Examples 401 to 404, 407 to 410 andComparative Application Examples 401 to 405, Table 7 and FIG. 31 showthe emission efficiency and the NTSC ratio (i.e., value in the u′-v′chromaticity coordinate system on the CIE1976 chromaticity diagram)measured through a diffuser and color filters, whose transmissionspectra are shown in FIG. 30.

TABLE 7 Emission efficiency (lm/W) NTSC ratio (%) Ap. Ex. 401 28.6 89.0Ap. Ex. 402 27.2 89.7 Ap. Ex. 403 31.8 88.5 Ap. Ex. 404 30.6 89.0 Ap.Ex. 407 33.2 88.4 Ap. Ex. 408 33.0 88.3 Ap. Ex. 409 32.8 86.7 Ap. Ex.410 32.3 86.9 Com. Ap. 401 40.3 82.8 Com. Ap. 402 37.1 83.4 Com. Ap. 40329.7 84.8 Com. Ap. 404 29.6 85.0 Com. Ap. 405 14.6 86.4

The above results indicate that it was difficult for the modules ofComparative Application Examples 401 to 405, which adopted conventionalfluorescent substances, to realize both high emission efficiencies andlarge NTSC ratios. On the other hand, however, the results also indicatethat the modules of Application Examples 401 to 404 and 407 to 410according to the embodiment realized both high emission efficiencies andlarge NTSC ratios, as compared with those of Comparative ApplicationExamples.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel methods and systems describedherein may be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the methods andsystems described herein may be made without departing from the spiritof the inventions. The accompanying claims and their equivalents areintended to cover such forms or modifications as would fail within thescope and spirit of the inventions.

The invention claimed is:
 1. A light-emitting device comprising: alight-emitting element to emit light, and a fluorescent substance (R)giving off luminescence under excitation by light of said light emittingelement, wherein the fluorescent substance R is represented by thefollowing formula (1):(M_(1-x)EC_(x))_(a)M¹ _(b)AlO_(c)N_(d)  (1) in which M is an elementselected from the group consisting of IA group elements, IIA groupelements, IIIA group elements, IIIB group elements, rare earth elementsand IVA group elements; EC is an element selected from the groupconsisting of Eu, Ce, Mn, Tb, Yb, Dy, Sm, Tm, Pr, Nd, Pm, Ho, Er, Cr,Sn, Cu, Zn, As, Ag, Cd, Sb, Au, Hg, Tl, Pb, Bi and Fe; M¹ is differentfrom M and is selected from the group consisting of tetravalentelements; and x, a, b, c and d are numbers satisfying the conditions of0<x<0.2, 0.63<a<0.80, 2.1<b<2.63, 0≦c≦0.24 and 4≦d≦5, respectively; andemitting luminescence having a peak in the wavelength range of 620 to670 nm under excitation by light in the wavelength range of 250 to 500nm.
 2. The device according to claim 1, wherein said light-emittingelement emits light in the wavelength range of 250 to 500 nm, andfurther comprising another fluorescent substance (Y) that gives offluminescence having a peak in the wavelength range of 540 to 580 nmunder excitation by light of said light-emitting element.
 3. The deviceaccording to claim 2, wherein said fluorescent substance (Y) is selectedfrom the group consisting of YAG phosphor, (Sr,Ca,Ba,Eu)₂SiO₄,(Sr,Ca,Ba,Eu)₃SiO₅, (CaEu)Ga₂S₄, and α-SiAlon phosphor.
 4. The deviceaccording to claim 1, wherein said light-emitting element emits light inthe wavelength range of 250 to 430 nm, further comprising anotherfluorescent substance (Y) that gives off luminescence having a peak inthe wavelength range of 540 to 580 nm under excitation by light of saidlight-emitting element, and still another fluorescent substance (B)gives off luminescence having a peak in the wavelength range of 400 to490 nm under excitation by light of said light-emitting element.
 5. Thedevice according to claim 4, wherein said fluorescent substance (Y) isselected from the group consisting of YAG phosphor, (Sr,Ca,Ba,Eu)₂SiO₄,(Sr,Ca,Ba,Eu)₃SiO₅, (CaEu)Ga₂S₄, and α-SiAlon phosphor.
 6. The deviceaccording to claim 4, wherein said fluorescent substance (B) is selectedfrom the group consisting of (Ba,Eu)MgAl₁₀O₁₇, (Sr,Ca,Ba,Eu)₁₀(PO₄)₅Cl₂and (Sr,Eu)Si₉Al₁₉ON₃₁.
 7. The device according to claim 1, wherein saidlight-emitting element emits light in the wavelength range of 250 to 500nm, and further comprising another fluorescent substance (G) that givesoff luminescence having a peak in the wavelength range of 490 to 540 nmunder excitation by light of said light-emitting element.
 8. The deviceaccording to claim 1, wherein said light-emitting element emits light inthe wavelength range of 250 to 430 nm, further comprising anotherfluorescent substance (G) that gives off luminescence having a peak inthe wavelength range of 490 to 540 nm under excitation by light of saidlight-emitting element, and still another fluorescent substance (B) thatgives off luminescence having a peak in the wavelength range of 400 to490 nm under excitation by light of said light-emitting element.
 9. Thedevice according to claim 8, wherein said fluorescent substance (B) isselected from the group consisting of (Ba,Eu)MgAl₁₀O₁₇,(Sr,Ca,Ba,Eu)₁₀(PO₄)₅Cl₂ and (Sr,Eu)Si₉Al₁₉ON₃₁.
 10. A light-emittingdevice module comprising a plural number of the devices according toclaim 1 and a substrate on which said plural devices are placed.
 11. Themodule according to claim 10, satisfying the condition of 1≦(d/a)≦5 inwhich a is the longitudinal length of each of said devices and d is theshortest interval between neighboring two of said devices.
 12. Thedevice according to claim 1, wherein said M¹ in the formula (1) is Si.13. The device according to claim 1, wherein said M in the formula (1)is an element selected from the group consisting of Li, Na, K, Mg, Ca,Sr, Ba, B, In, Ga, Y, Sc, Gd, La, Lu and Ge.
 14. The device according toclaim 1, wherein said b in the formula (1) is a number satisfying thecondition of 2.1<b<2.5.
 15. The device according to claim 1, whereinsaid c in the formula (1) is a number satisfying the condition of0.05<c≦0.21.